This invention relates to ultrasonic scan and display apparatus, and has particular application to a B-scan unit utilizing an ultrasonic transducer that moves back and forth in an arcuate path.
Ultrasonic scan and display apparatus is known, utilizing an ultrasonic transducer that moves back and forth in an arcuate path at a relatively low frequency, pulsed at a relatively high frequency to generate ultrasonic pulses which enter into an object that is being scanned, e.g., a small organ of the human body or the human eye. Echo pulses from the object scanned are received by the transducer and displayed on a cathode ray tube screen to provide highly useful information regarding the scanned object. Since the cathode ray tube utilizes orthogonal beam deflection, it has been recognized in the past that it is necessary to provide special signals to the beam deflection electrodes in the cathode ray tube to produce a beam trace on the screen of that tube that conforms to the sector scanned by the ultrasonic transducer. Holasek and Sokollu have described in an article published in 1972 Ultrasonics Symposium Proceedings, "Direct Contact, Hand-Held, Diagnostic B-Scanner" a beam deflection circuit for a cathode ray tube utilizing sine and cosine signals, and particularly first-order simulation of sine and cosine functions. Eggleton et al U.S. Pat. No. 3,974,826, issued Aug. 17, 1976, discloses the use of sine and cosine beam deflection signals; in this case, a function generator, such as a Burr Brown sine cosine function generator, is used.
The present invention utilizes sine and cosine signals for appropriate development of a distortion-free sector display in a cathode ray tube incorporating orthogonal beam deflection. The invention recognizes that the sine function may be approximated by the angle itself, that is, sine .theta..about..theta. for small angles (the relative angular position of the ultrasonic transducer in its arcuate path with respect to a reference position), and the following function as representing the cosine function: EQU cosine .theta..about.1-.theta..sup.2 /2.
Signals representing .theta. and 1-.theta..sup.2 /2 are stored on relatively high capacitance capacitors and then gated onto lower capacitance capacitors as initial values, from which ramp functions are generated to provide the X and Y sweeps of the beam in the cathode ray tube. Elaborate circuitry is avoided, and a simple but highly effective circuit functions to provide appropriate X and Y sweeps to provide a relatively distortion-free sector display in the cathode ray tube.
The invention will be more completely understood by reference to the following detailed description.